The present invention relates to an improved orbital vibrator. More particularly, the present invention relates to an orbital vibrator of the type used to generate seismic reference signals in geophysical prospecting systems.
The use of orbital vibrators as seismic waveform generators is well known in the area of geophysical prospecting for oil, or the like. Typically, the vibrators take the form of eccentric swinging weights which are used in various combinations to generate the desired seismic signal(s). See for example U.S. Pat. Nos. 2,745,507; 2,989,869; and 4,234,053.
In order to generate a seismic signal of sufficient magnitude, these swinging weights must be of appreciable mass and be rotated at rates which may exceed 3000 r.p.m. Accordingly, these weights are subjected to large internal pressures as a result of centrifugal force. Further, the drag due to wind resistance (composed of frontal area drag and skin friction components) increase these internal pressures and decrease the efficiency of the system. Accordingly, these orbital vibrators must be constructed of exotic, and hence expensive, high strength materials.
It is an object of the present invention to provide an improved orbital vibrator which will overcome these deficiencies. The orbital vibrator of the present invention comprises a hollow cylindrical reaction mass which is mounted by means of a bearing on a crank shaft. The eccentricity of the crank causes the reaction mass to orbitally oscillate about the center line of the shaft in response to the shaft's rotation. Since there is no leading edge on the weight of the present invention, there is a significant reduction in frontal area drag. The fact that the orbital vibrator does not rotate at high speed but rather orbitally oscillates serves to further reduce drag losses resulting from the skin friction component. The reduction of the internal pressures to which the orbital vibrator is exposed enables a less expensive material to be used.
These and other features, characteristics and advantages of the present invention will become apparent after reading the following specification.